1. Field of the Invention
The present invention relates to a communication control method, and more particularly to a communication control method in a digital mobile communication apparatus of TDMA/TDD (Time Division Multiple Access/Time Division Duplex) system.
2. Description of Related Art
In accordance with a frame format used in a digital mobile communication apparatus of the TDMA/TDD system, one frame comprises as follows, as shown in FIG. 1.
(1) A down link access channel A1.sub.DOWN and an up link access channel A2.sub.UP having a function as an access channel Ach used for communication of control information to establish frame synchronization of a mobile machine to a base station and to shift from the access channel Ach to a control channel Cch.
(2) Down link control channels C1.sub.DOWN -C8.sub.DOWN and up link control channels C9.sub.UP -C16.sub.UP having a function as a control channel Cch used for communication of control information to communicate data in a user channel Uch.
The down link control channels and the up link control channels are used in a combination such as a down link control channel C1.sub.DOWN and an up link control channel C9.sub.UP, and a down link control channel C2.sub.DOWN and an up link control channel C10.sub.UP.
(3) User channels U1-U64 having a function as a user channel Uch used for communication of data.
The user channel Uch is allocated for the down link and the up link separately for each slot. The base station indicates to the mobile machine by using the control channel Cch the particular slot used for the up link and the particular slot used for the down link in accordance with the data amounts of the up link and the down link to conduct the communication with the mobile machine.
Referring to FIG. 2, a start protocol of the communication when such a frame format is used is explained. The mobile machine receives the down link access channel A1.sub.DOWN to establish the frame synchronization to the base station. Thus, the mobile machine may determine the particular slot used at the particular time in the base station. The mobile machine registers by using the up link access channel A2.sub.UP. The base station transmits a communication start request by using the down link access channel A1.sub.DOWN and the mobile machine transmits the communication start request by using the up link access channel A2.sub.UP. When the communication start request is communicated, the base station designates an available control channel Cch to the mobile machine by using the down link access channel A1.sub.DOWN. In this instance, a combination of the down link access channel C1.sub.DOWN and the up link access channel C9.sub.UP is designated as the available control channel Cch. The mobile machine sends back an acknowledgement (ACK) thereto by using the up link access channel A2.sub.UP. At this time, the access channel Ach is released. In the example shown in FIG. 2, the control channel Cch is designated by using the down link access channel A1.sub.DOWN but since there is only one set of access channel Ach in one slot, an N-channel super frame structure is adopted and a plurality of mobile machines are accommodated without conflict. Thereafter, the user channel Uch designation is indicated from the base station to the mobile machine by using the down link control channel C1.sub.DOWN. In this instance, three user channel U1-U3 are allocated for the down link and two user channels U4 and U5 are allocated for the up link. The mobile machine sends back the acknowledgement (ACK) to the base station by using the up link control channel C9.sub.UP. Thereafter, the communication is conducted by using the user channel Uch. Thereafter, the procedure of communication by designating the user channel Uch to be used by the control channel Cch and communicating by using the user channel Uch is repeated, and the communication is terminated by the control channel Cch, the access channel Ach of the super frame structure is received and the start of next communication is waited. The communication is conducted in such a protocol.
In the above communication control method, since there are eight sets of communication channel Cch, concurrent communication may be conducted for eight mobile machines. When all slots are busy, the information to be communicated are classified to priority data and non-priority data and the mobile machine which communicates only the non-priority data is controlled to the waiting state, and the mobile machine which communicates the priority data is controlled to be allocated with the control channel Cch. This control method is described below.
The mobile machine which communicates the priority data (referred to as a second mobile machine #2) issues a communication request to the base station by using the up link access channel A2.sub.UP. The base station transmits wait information to the mobile machine which communicates the non-priority data (referred to as a first mobile machine #1). When the first mobile machine #1 receives the wait information, it releases the control channel Cch and reacquires the access channel (Ach) synchronization to receive the super frame, and waits for the start of communication. The base station notifies the allocation of the control channel Cch by using the down link access channel A1.sub.DOWN. For this notice, the second mobile machine #2 sends back the acknowledgement (ACK) to the base station. Thereafter, it communicates the allocation information of the user channel Uch by using the control channel Cch to conduct the communication of information by the user channel Uch.
As described above, in the prior art communication control method, the mobile machine which communicates the non-priority data is controlled to the waiting state and the control channel Cch is allocated to the mobile machine which communicates the priority data so that the number of secured mobile machines which communicate the priority data is increased. Further, the waiting mobile machine receives the access channel Ach of the super frame structure so that the power consumption during the waiting is reduced. However, the waiting mobile machine must wait until it receives the access channel Ach of the super frame structure even if the control channel Cch becomes available, and the utilization efficiency of the control channel Cch is lowered.